For the inspection of workpieces or components, induction thermography may be used as an inspection method. In this case, a temperature profile, for example on a surface of the object to be inspected, is acquired with an infrared camera in a multiplicity of images. In general, distinction is made between active thermography (with stimulation) and passive thermography (without stimulation). In this case, induction thermography constitutes an active method.
In induction thermography, an induction current is generated by means of a coil, or an inductor, in the object to be inspected. This leads to heating of the object by ohmic losses, so that a thermal profile can be detected by means of the infrared camera from a resulting heat distribution on the surface of the object.
If the object to be inspected has defects, in particular cracks, then the induced current must flow around these or through individual contact positions of the crack edges. For this reason, a local current density and therefore heating due to ohmic losses is increased at the defects, for example at the cracks. This increased heating of the defects is visible in the infrared image.
For inspection of the object, it is necessary to bring the coil particularly close to the object, since the induced current flows preferentially in the vicinity of the coil. For this reason, however, only local inspection in a particular region of the object can take place. If the entire object or a wide-ranging region of the object is intended to be studied, the measurement must be repeated several times, that is to say from different acquisition directions with corresponding displacement of the coil. According to the prior art, for each individual measurement the multiplicity of images are subjected to a mathematical analysis, which delivers a result image for each measurement. Typically, depending on the size of the object to be inspected, about 80 images (result images) are generated, which need to be observed and analyzed individually by a tester. Because of such individual observation by the tester, the defect detectability is impaired, since typically only a small section of the thermographic image respectively contains essential information while as a result of the analysis the rest of the image has a high level of noise or shows no signal, and therefore no information. Furthermore, individual defects may readily be visible in images of a plurality of measurements, which can lead to inefficient multiple observation of the same defect.